NCERT Solutions Curiosity Chapter 7 Chapter exercises — Let us enhance our learning

Book page 137 to 140 Updated on2026-09-05

Q1.

The normal temperature of a healthy human being is close to _______ . (i) 98.6 °C (ii) 37.0 °C (iii) 32.0 °C (iv) 27.0 °C

Answer

Answer: (ii) 37.0 °C

Why the others are wrong:

(i) 98.6 °C — 98.6 is the correct number, but on the Fahrenheit scale. Written as 98.6 °C it would be a temperature close to boiling water. Watch the unit.
(iii) 32.0 °C — far below the human range, which does not normally go below 35 °C.
(iv) 27.0 °C — this is a pleasant room temperature, not a body temperature.

Tip: 37.0 °C and 98.6 °F are the same temperature. The number changes with the scale, so always write the unit — this question is testing exactly that.

Q2.

37 °C is the same temperature as _______ . (i) 97.4 °F (ii) 97.6 °F (iii) 98.4 °F (iv) 98.6 °F

Answer

Answer: (iv) 98.6 °F

The book states it directly: a temperature measured as 37.0 °C on the Celsius scale is equivalent to 98.6 °F on the Fahrenheit scale.

You can also check it with the conversion rule:

Temperature in °F = (9/5) × temperature in °C + 32
= (9/5) × 37 + 32
= 9 × 37 ÷ 5 + 32
= 333 ÷ 5 + 32
= 66.6 + 32
= 98.6 °F

Did you know? On the Kelvin scale the same temperature is 37 + 273.15 = 310.15 K — no degree sign with K.

Q3.

Fill in the blanks: (i) The hotness or coldness of a system is determined by its _______ . (ii) The temperature of ice-cold water cannot be measured by a _______ thermometer. (iii) The unit of temperature is degree _______ .

Answer

Blank	Answer
(i) The hotness or coldness of a system is determined by its …	temperature
(ii) The temperature of ice-cold water cannot be measured by a … thermometer	clinical
(iii) The unit of temperature is degree …	Celsius

(i) Temperature is the reliable measure of hotness or coldness — touch is not.

(ii) Ice-cold water is at about 0 °C, well below the 35 °C at which a clinical thermometer’s scale begins, so a clinical thermometer cannot measure it. A laboratory thermometer (–10 °C to 110 °C) can.

(iii) On the Celsius scale the unit is degree Celsius (°C). (On the Fahrenheit scale it is degree Fahrenheit, °F; the SI unit, however, is the kelvin, K, which takes no degree sign.)

Tip: The book has a special note on writing units — “degree” starts with a small letter, but “Celsius” and “Fahrenheit” start with capitals, and a space is left between the number and the unit: 37.0 °C, not 37.0°C.

Q4.

The range of a laboratory thermometer is usually _______ . (i) 10 °C to 100 °C (ii) –10 °C to 110 °C (iii) 32 °C to 45 °C (iv) 35 °C to 42 °C

Answer

Answer: (ii) –10 °C to 110 °C

Why this range: a laboratory thermometer must handle the whole of ordinary laboratory work — ice at 0 °C, cold water below that, room air, warm water and water boiling at about 100 °C. So the scale is carried a little below 0 °C and a little above 100 °C, giving a total span of 110 – (–10) = 120 °C.

Why the others are wrong:

(i) 10 °C to 100 °C — could not measure ice, and could not quite reach boiling.
(iii) 32 °C to 45 °C and (iv) 35 °C to 42 °C — these are body-temperature ranges. (iv) in particular is the range of a clinical thermometer.

Q5.

Four students used a laboratory thermometer to measure the temperature of water as shown in Fig. 7.6. Who do you think followed the correct way for measuring temperature? (i) Student 1 (ii) Student 2 (iii) Student 3 (iv) Student 4

Answer

Answer: (ii) Student 2

Looking carefully at each picture in Fig. 7.6:

Student	What the picture shows	Correct?
Student 1	Thermometer held slanting, resting against the beaker with the bulb at the bottom	✗ Tilted, and the bulb touches the beaker
Student 2	Thermometer vertical, bulb well inside the water, clear of the bottom and the sides	✓ Correct
Student 3	Thermometer vertical, but the bulb rests on the bottom of the beaker	✗ Bulb touching the bottom
Student 4	Thermometer leaning on the rim, bulb barely at the water surface, not properly immersed	✗ Bulb not fully in the water

The book’s three rules for the correct way are all satisfied only by Student 2:

the bulb should not touch the bottom or the sides of the beaker;
the thermometer should be held vertically, not tilted;
the temperature must be read while the thermometer is immersed in the water — and while reading, the eye should be directly in line with the top of the liquid column.

Reading a laboratory thermometer. The eye must be exactly in line with the top of the liquid column; looking from above or from below gives a wrong reading. The bulb stays fully in the water but does not touch the bottom or the sides.

Why touching the bottom is wrong: the bottom of the beaker may be hotter or colder than the water itself. Resting the bulb there makes the thermometer measure the glass, not the water.

Q6.

Colour to show the red column on the drawings of thermometers (Fig. 7.7) as per the temperatures written below: 14 °C, 17 °C, 7.5 °C

Answer

First look at each scale, because the three thermometers of Fig. 7.7 are not divided alike. All three are marked from –10 °C to 30 °C, but:

Thermometer	Divisions between 0 °C and 10 °C	One small division	Temperature to colour
First	5	2 °C	14 °C
Second	10	1 °C	17 °C
Third	20	0.5 °C	7.5 °C

Now colour the column red from the bulb up to the correct mark:

14 °C on the first thermometer — 2 divisions above the 10 °C mark (10 + 2 + 2 = 14).
17 °C on the second — 7 divisions above the 10 °C mark.
7.5 °C on the third — 15 divisions above the 0 °C mark (15 × 0.5 = 7.5).

Answer to Question 6. The red column is filled up to 14 °C, 17 °C and 7.5 °C. The third scale can show 7.5 °C only because its smallest division is 0.5 °C.

Why the three scales are different: the question is quietly teaching that a temperature can only be shown on a thermometer whose smallest division allows it. 7.5 °C cannot be marked on the first thermometer at all — its marks jump 2 °C at a time.

Q7.

Observe the part of thermometer shown in Fig. 7.8 and answer the following questions: (i) What type of thermometer is it? (ii) What is the reading of the thermometer? (iii) What is the smallest value that this thermometer can measure?

Answer

(i) It is a laboratory thermometer.

You can tell from the scale itself: it is marked from below 0 °C (the first label is –10) up past 40 °C. A clinical thermometer would begin at about 35 °C and stop at 42 °C, and would never show negative temperatures.

(ii) The reading is 26 °C.

The red liquid column has crossed the 20 °C mark.
Count the small divisions past 20 °C: 21, 22, 23, 24, 25, 26 — the column ends at the sixth one.
Reading = 26 °C

Fig. 7.8 redrawn. Ten small divisions fit between 0 °C and 10 °C, so one division = 1 °C. The red column stops at the sixth mark after 20 °C — the reading is 26 °C.

(iii) The smallest value it can measure is 1 °C.

Difference between two numbered marks (0 °C and 10 °C) = 10 °C
Number of small divisions between them = 10
One small division = 10 °C ÷ 10 = 1 °C

Tip: Always answer part (iii) before part (ii). Once you know that one division is 1 °C, counting divisions gives the reading straight away.

Q8.

A laboratory thermometer is not used to measure our body temperature. Give a reason.

Answer

Reason: a laboratory thermometer has no kink above its bulb, so the liquid column begins to fall the moment the thermometer is taken out of the mouth — the reading is lost before it can be read.

The older mercury clinical thermometer. Its scale covers only 35 °C to 42 °C — the range of human body temperature. The kink just above the bulb stops the mercury from running back, so the reading stays put after the thermometer is taken out. (On a real one each small division is 0.1 °C; only the 0.2 °C marks are drawn here.)

Any one of these is an acceptable reason; together they make the case complete:

No kink — the reading does not stay put, and a laboratory thermometer cannot be read while it is inside the mouth.
Too coarse — its smallest value is usually 1 °C, while body temperature has to be known to 0.1 °C. A rise from 37.0 °C to 37.6 °C is a real fever, and a laboratory thermometer simply cannot show it.
Wrong range for the job — its scale is spread over 120 °C (–10 °C to 110 °C), so the few degrees that matter for the body are squeezed into a tiny part of the scale.
Shape and safety — it is long, straight and fragile, and is not designed to be put into a person’s mouth or armpit.

How the kink solves this: the kink is a narrow constriction in the tube just above the bulb. While the thermometer is warming, the expanding mercury is pushed past it. When the thermometer is removed and the mercury cools and contracts, the thread breaks at the kink, so the mercury above it cannot slide back — the reading stays until you shake it down.

Q9.

Vaishnavi has not gone to school as she is ill. Her mother has kept a record of her body temperature for three days as shown in Table 7.4. (i) What was Vaishnavi’s highest recorded temperature? (ii) On which day and at what time was Vaishnavi’s highest temperature recorded? (iii) On which day did Vaishnavi’s temperature return to normal?

Answer

Table 7.4 again, with the highest value of each day marked:

DAY	7am	10am	1pm	4pm	7pm	10pm
One	38.0 °C	37.8 °C	38.0 °C	38.0 °C	40.0 °C	39.0 °C
Two	38.6 °C	38.8 °C	39.0 °C	39.0 °C	39.0 °C	38.0 °C
Three	37.6 °C	37.4 °C	37.2 °C	37.0 °C	36.8 °C	36.6 °C

(i) The highest recorded temperature was 40.0 °C. Scanning all eighteen readings, the largest is 40.0 °C; the next largest are the three readings of 39.0 °C on Day Two.

(ii) It was recorded on Day One at 7 pm.

(iii) On Day Three.

Normal body temperature = 37.0 °C
Day Three readings: 37.6 → 37.4 → 37.2 → 37.0 → 36.8 → 36.6 °C
The temperature comes down steadily and touches 37.0 °C at 4 pm, then stays at or below it.
So Vaishnavi’s temperature returned to normal on Day Three.

Reading the pattern: Day One and Day Two are the fever days — every reading is above 38 °C except one. On Day Three not a single reading crosses 38 °C and the whole day slopes downwards, which is how a fever settles.

Tip: Notice how much the temperature moves during a single day — 37.8 °C at 10 am and 40.0 °C at 7 pm on Day One. This is why a doctor asks for temperature to be recorded several times a day, not once.

Q10.

If you have to measure the temperature 22.5 °C, which of the following three thermometers will you use (Fig. 7.9)? Explain.

Answer

Answer: thermometer (b).

All three thermometers in Fig. 7.9 carry the same scale from –10 °C to 30 °C, so all three reach 22.5 °C. What differs is how finely each is divided. Counting the small divisions between 0 °C and 10 °C on each:

Thermometer	Divisions between 0 °C and 10 °C	One small division	Can it show 22.5 °C?
(a)	10	1 °C	No — only 22 °C or 23 °C
(b)	20	0.5 °C	Yes
(c)	5	2 °C	No — only 22 °C or 24 °C

For (b): one small division = 10 °C ÷ 20 = 0.5 °C
22.5 °C = 20 °C + 5 divisions of 0.5 °C
So 22.5 °C falls exactly on a mark of thermometer (b).

Explanation to write: a thermometer can only be read to its smallest division. Thermometer (b) has the finest divisions, 0.5 °C, and 22.5 °C lands exactly on one of its marks. On (a) 22.5 °C lies halfway between two marks, and on (c) it lies between 22 °C and 24 °C — neither can show it correctly.

Q11.

The temperature shown by the thermometer in Fig. 7.10 is (i) 28.0 °C (ii) 27.5 °C (iii) 26.5 °C (iv) 25.3 °C

Answer

Answer: (ii) 27.5 °C

Work out the smallest value first, then count.

Numbered marks on Fig. 7.10: 0, 5, 10, 15, 20, 25, 30, 35, 40
Difference between two numbered marks = 5 °C
Small divisions between them = 10
One small division = 5 °C ÷ 10 = 0.5 °C

The red column ends past the 25 mark.
Divisions counted after 25: 25.5, 26.0, 26.5, 27.0, 27.5 — five divisions.
Reading = 25 °C + 5 × 0.5 °C = 27.5 °C

Fig. 7.10 redrawn. Ten small divisions fit between 25 °C and 30 °C, so one division = 0.5 °C. The column ends five divisions past 25 °C, that is at 27.5 °C.

Why the others are wrong: 28.0 °C is one division too far; 26.5 °C is two divisions short; and 25.3 °C could never be read at all on this thermometer, because 0.3 is not a multiple of its smallest division of 0.5 °C.

Q12.

A laboratory thermometer has 50 divisions between 0 °C and 100 °C. What does each division of this thermometer measure?

Answer

Use the same rule as in Activity 7.4.

One division = temperature difference ÷ number of divisions
Temperature difference = 100 °C – 0 °C = 100 °C
Number of divisions = 50
One division = 100 °C ÷ 50
= 2 °C

So each division of this thermometer measures 2 °C.

What that means: this thermometer is a coarse one. It can show 24 °C or 26 °C, but never 25 °C — there is no mark there. Its smallest value is 2 °C.

Check it yourself: the usual laboratory thermometer of Fig. 7.3b has 10 divisions in each 10 °C, giving 1 °C per division. To get 0.5 °C per division you would need 20 divisions in each 10 °C.

Q13.

Draw the scale of a thermometer in which the smallest division reads 0.5 °C. You may draw only the portion between 10 °C and 20 °C.

Answer

First decide how many divisions are needed.

Length of the portion to be drawn = 20 °C – 10 °C = 10 °C
Each smallest division must read 0.5 °C
Number of divisions = 10 °C ÷ 0.5 °C = 20 divisions

How to draw it:

Draw a straight line and mark two points on it, 10 cm apart. Label the left one 10 °C and the right one 20 °C.
Divide the 10 cm into 20 equal parts — that is, put a mark every 5 mm. This gives 19 marks in between, making 20 divisions in all.
Draw the marks at whole degrees (11, 12, 13 … 19) a little longer, and write the numbers under them. The short marks in between stand for the half degrees 10.5, 11.5, 12.5 and so on.
Each smallest division now reads 0.5 °C.

Answer to Question 13 — the part of a scale between 10 °C and 20 °C, cut into 20 equal parts, so each smallest division reads 0.5 °C. The column drawn here reads 16.5 °C.

Tip: Choose a length that divides easily. 10 cm for 10 °C is ideal, because every 0.5 °C then becomes a neat 5 mm on your ruler.

Q14.

Komal tells you that she has a fever of 101 degrees. Does she mean it on the Celsius scale or Fahrenheit scale?

Answer

She means 101 degrees Fahrenheit, that is 101 °F — on the Fahrenheit scale.

Why it cannot be Celsius: the temperature of human beings does not normally go below 35 °C or above 42 °C. A body temperature of 101 °C is impossible — water itself boils at about 100 °C. So 101 has to be a Fahrenheit reading.

How high a fever is 101 °F? Compare it with normal:

Normal = 98.6 °F = 37.0 °C
Komal’s temperature = 101 °F
Rise above normal = 101 – 98.6 = 2.4 °F
In Celsius: (101 – 32) × 5/9 = 69 × 5 ÷ 9 = 345 ÷ 9 = 38.3 °C (rounded to one decimal place)

So Komal has a fever of about 38.3 °C — a moderate fever, about 1.3 °C above normal.

Tip: Many people in India still quote fever in °F out of habit, because the old mercury thermometers were marked in Fahrenheit. When someone says “100 degrees fever”, they always mean °F. Writing the unit removes all doubt.

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